1. Field of the Invention
The invention relates to a semiconductor device which is used as an LED (Light Emitting Diode) array or the like, an LED printhead including the semiconductor device, and an image forming apparatus.
2. Description of the Related Art
In an image forming apparatus of an electrophotographic system, an LED printhead obtained by combining an LED array chip in which a number of LEDs are arranged and a driver chip provided with a driving circuit is used.
In such a kind of image forming apparatus, since high resolution is required, an LED printhead obtained by mounting a plurality of LED array chips and a plurality of driver chips onto a supporting board or a printed circuit board is used.
To reduce the number of chips to be mounted, there has been proposed a semiconductor device having such a structure that a semiconductor thin film on which LED elements have previously been provided is fixed onto a semiconductor substrate on which a driving circuit has been formed and each of the LED elements and the driving circuit are electrically connected by a wiring pattern (refer to JP-A-2004-179641).
In such a semiconductor device, in order to provide wirings, an inter-layer insulating film made of a material of SiN or the like is provided on the semiconductor thin film. However, in this case, since it is necessary to provide a contact electrode for electrically connecting a contact layer of the semiconductor thin film and the wirings, an opening portion for exposing the contact layer has been formed in the inter-layer insulating film.
However, as for the opening portion provided in the inter-layer insulating film, since its edge portion is formed from the orthogonally-crossing surface which rises in the thickness direction, stresses which are applied from the contact electrode and the inter-layer insulating film are concentrated near the opening portion and there is a risk that a crack occurs in the semiconductor thin film or the contact electrode formed in the opening portion is peeled off from the edge portion of the opening portion.